The invention relates to a towing vehicle for shunting airplanes on the ground, with a U-shaped recess in the rear part of the towing vehicle for reception of a front wheel assembly which is turnable about a substantially vertical axis, a holding- and lifting device at each side of the U-shaped recess of the towing vehicle and comprising gripper arms serving to engage the front wheel assembly in the region of the periphery or peripheries of the front wheel or wheels, the rear gripper arms being pivotable as a pair inwardly and outwardly in a vertical plane which is disposed at right angles to the longitudinal axis of the towing vehicle, an adjusting device which conforms the gripper arms to the diameters of the respective front wheels, the turning axis of the front wheel assembly crossing at right angles the axis of the rear wheels of the towing vehicle.
Heretofore, it was necessary to provide five different towing vehicles for five aircraft types which differ from each other as to weight and size. The next development includes tractors which manipulate the aircraft without a towing bar. Such a tractor is described, for example, in the published German patent application 36 16 807 and has a lifting shovel onto which the front wheel assembly of the aircraft must be pushed or pulled. At such time, the aircraft is in motion with its brakes released, whereas the towing vehicle is braked.
The same problem arises in a towing vehicle according to the published German patent application 38 01 855. In this conventional design, the rear part of the towing vehicle has a U-shaped recess for a lifting shovel which is lowered to the ground and onto the supporting surface of which the front wheel assembly is thereafter pulled with assistance from a gripping- and pulling device. It is again necessary to move the aircraft during coupling to the towing vehicle, and such movement is likely to take place in a direction in which undesirable forces are likely to act upon the front wheel assembly.
In an embodiment of the towing vehicle according to the published German patent application 38 01 855, the lifting shovel is not only movable up and down but is also pivotable and tiltable with reference to a pendulum point. The means for supporting the lifting shovel comprises longitudinal, transverse and parallelogram linkages as well as piston-cylinder-units which permit the lifting shovel to perform a plurality of movements about a variety of axes in the transverse and longitudinal directions of the vehicle.
In certain types of aircraft the axis of the front wheel assembly is forwardly inclined with respect to the vertical so that, when the aircraft moves in a curve, the axis of the wheel becomes inclined to the horizontal. In such instances, the lifting shovel is likely to be tilted about the pendulum point to thus ensure a gentle towing operation. However, in view of the numerous degrees and possibilities of freedom, the conventional design according to the published German patent application 31 01 855 is relatively complex a to its construction and controls because all movements of the lifting shovel must be positively controlled or guided which does not ensure tension-free towing away under all circumstances.
U.S. Pat. No. 43 75 244 discloses an analogous towing vehicle wherein the front wheel assembly can be accepted while the towing vehicle as well as the aircraft are at a standstill and, therefore, the aforedescribed negative influences of forces do not develop at all. However, this conventional design also exhibits the drawback that, in the event of changes of inclination between the axis of the wheel of the front wheel assembly and the rear wheel axis of the towing vehicle, such as develop for example during travel on uneven ground, the front wheel assembly is acted upon by undesirable forces.